JPS61191575A - Porous silicon carbide sintered body and manufacture - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a porous tube silicon carbide sintered body and a method for manufacturing the same.
In particular, the present invention relates to a porous tubular silicon carbide sintered body having a transition layer in which the average cross-sectional area of open pores of a three-dimensional network structure mainly composed of silicon carbide plate crystals changes continuously, and a method for manufacturing the same.

Traditionally, silicon carbide has high hardness, good wear resistance, good oxidation resistance, good corrosion resistance, good thermal conductivity, low coefficient of thermal expansion, high r# thermal shock resistance and high strength at high temperatures. It has excellent chemical and physical properties such as mechanical seals and bearings, wear-resistant materials such as refractory materials for high-temperature furnaces, heat-resistant structural materials such as heat exchangers, combustion tubes, acids and alkalis, etc. It is a material that can be widely used as a corrosion-resistant material for pump parts for solutions with strong corrosive properties.

Therefore, a porous silicon carbide sintered body that has these excellent properties and has open pores, that is, pores that conduct electricity to the outside (hereinafter simply referred to as pores), is a porous silicon carbide sintered body that has these excellent properties. Taking advantage of its characteristics, it is a material that can be used as a filter filter used in high temperature atmospheres, oxidizing atmospheres and/or corrosive atmospheres, catalysts or catalyst supports for oxidative exothermic reactions or chemical reactions at high temperatures, For example, sludge or sulfuric acid mixed in the plating solution, j! It is conceivable that it can be used as a filter used to remove foreign particles mixed in corrosive liquids such as acids.

For the above-mentioned use of the 1l letter, simply 1l
In addition to being required to have heat resistance and corrosion resistance, it is also required to have characteristics such as low resistance when fluid passes through it, the ability to remove foreign particles with high efficiency, and a long service life.

On the other hand, for applications such as catalysts, catalyst supports, or heat exchangers, it is important to have a large surface area that can effectively generate chemical reactions, heat transfer, or mass transfer. It is required to be stable and hard to cause clogging.

[Conventional technology]

Conventionally, as a method for manufacturing a porous silicon carbide sintered body, (1)
A method of manufacturing by mixing coarse silicon carbide particles and fine silicon carbide particles, molding the mixture, and then firing it in a high temperature range equal to or higher than the recrystallization temperature of silicon carbide, (2) Disclosed in JP-A-48-39515 "By adding #j2 elemental binder to silicon carbide powder with or without addition of carbon powder, and adding a stoichiometric amount of silicone powder that reacts with this carbon powder and free carbon from the binder produced during firing. A method for producing a homogeneous porous recrystallized silicon carbide body, which comprises shaping the body, and then heating the body in carbon powder at 1900 to 2400°C to silicify the carbon content in the body. Alternatively, (3) a silicon carbide skeleton structure is disclosed in Japanese Patent Application Laid-Open No. 58-122016 by impregnating a polymeric foam material with a silicon carbide matrix slurry and removing the polymeric foam material by a rinsing treatment. 1900~2800″
Primary calcination in argon at a temperature of
Secondary firing is performed in nitrogen gas at 1 to 200 atm at a temperature of 600 to 2100°C, and then heat resistant on both ends! A method for producing a silicon carbide film capable of generating electricity by forming a pole and being able to conduct electricity. ” etc. are known.

However, if the structure of the porous silicon carbide sintered body produced by the above methods (1) and (2) is illustrated in Figure 2, it is coated with silicon carbide aggregate fA+ and aggregate. It is composed of a silicon carbide binder or carbonaceous binder +B+ that binds the aggregates together, and gaps (C1).The gaps (C1, or pores) are mostly determined by the arrangement of the aggregates during molding, and are formed in the sintered body. The porosity of the sintered body is about 30 to 40%, which is relatively small.For this reason, the resistance when fluid passes through these sintered bodies is extremely high.On the other hand, if the porosity of the sintered body is increased, According to these methods, relatively large pore diameter In order to form a sintered body with a cross-sectional area, a large aggregate is required, which reduces the number of contact points between the particles and reduces the bonding strength between the particles, resulting in a significantly low strength of the sintered body. On the other hand, in order to obtain a sintered body with pores having a relatively small cross-sectional area, the particle size composition of the aggregate should be changed to coarse particles, medium particles, and/or coarse particles.
Alternatively, it is necessary to appropriately mix the molded product with fine particles and mold it, and the porosity of the molded product becomes extremely small, and in extreme cases, some of the pores tend to become clogged. Therefore, the resistance when fluid passes through such a sintered body becomes extremely high. In addition, the structure of the sintered body produced by method (3) above is composed of large and small cellular frameworks called a so-called skeleton structure, so the cross-sectional area of the pores is relatively large. It has been difficult to produce a sintered body with a pore cross-sectional area.

[Problem that the invention seeks to solve]

By the way, all sintered bodies obtained by the above-mentioned method have relatively uniform pore diameters, and in particular particles with a wide particle size distribution are suspended from suspended particles and/or suspended gas. When applied as a ficitor for separating particles by filtration, not only the filtration speed is extremely slow, but also the filtration rate is easily clogged with a relatively small amount of filtration.

One possible way to correct the above-mentioned drawbacks is to use a sintered body with continuously varying pore diameters as a filter. A sintered body in which the value of the sintered body is continuously changed and a method for manufacturing the same have not been previously known.

[Means for solving problems]

By the way, the present inventor has previously proposed a porous silicon carbide sintered body that is permeable to the outside and has arbitrary pore diameters and porosity according to various uses, and is suitable for fluid separation, adsorption, and absorption. We have discovered a new method for manufacturing porous silicon dioxide sintered bodies that can effectively utilize mass transfer, heat transfer, chemical reactions, etc.
No. 12645 [a sintered body mainly made of silicon carbide, mainly composed of silicon carbide plate crystals having an average aspect ratio of 3 to 50 and an average length in the major axis direction of 0.5 to 1000 μm] The average cross-sectional area of open pores in the network structure is 2>E.
A porous silicon carbide sintered body having a diameter of 0.01 to 250000 μm. ” and the invention related to its manufacturing method.

Therefore, with the aim of solving the above-mentioned problems, the inventors of the present invention conducted further research on the porous vm silicon sintered body and its manufacturing method, and found that it is composed mainly of silicon carbide plate crystals. Porous IR with a transition at which the average cross-sectional area of open pores of a three-dimensional network structure changes continuously
The present invention has been completed by newly discovering a silicon carbide sintered body and a method for manufacturing the same.

The present invention is a sintered body mainly made of silicon carbide,
It has a three-dimensional network structure mainly composed of silicon carbide plate crystals with an average aspect ratio in the range of 3 to 50 and an average length in the major axis direction in the range of 0.5 to 1000 μm. , a porous silicon carbide sintered body characterized by having a transition layer in which the average cross-sectional area of the pores of the network structure changes continuously, and a method for producing the same.

The present invention will be explained in detail below.

Figure 1 is a scanning electron micrograph (75x magnification) of an example of the porous silicon carbide sintered body of the present invention (hereinafter referred to simply as the porous body). It is. 1st
As is clear from the figure, the porous body of the present invention has a three-dimensional network structure in which silicon carbide plate crystals with an aspect ratio of 4 to 12 are intricately intertwined in multiple directions, and the pores are continuous and linear. A transition layer t?, in which the cross-sectional area of the pores and the length of the silicon carbide plate-like crystals continuously change. Exists.

Nao, the aspect ratio of the silicon carbide plate crystals here (
R) is the ratio of the maximum length X) of each plate crystal observed in an arbitrary cross section of the sintered body and (Y), that is, it is a value expressed by R=X/Y.

The porous body of the present invention needs to have a three-dimensional network structure composed of silicon carbide plate crystals having an average aspect ratio of 3 to 50. The reason why the average aspect ratio of the porous body is set to 8 or more is that the pores formed by the silicon carbide plate crystals are larger than the volume occupied by the crystals, that is, the porous body has a high porosity. This is to accomplish this.

2. As shown in Fig. 2, the structure of the conventional porous expanded silicon sintered body is determined by the arrangement of the aggregate at the time of the bottom shape. Unlike, the aspect ratio of the crystal is only around 2 at most,
Does not have high porosity. On the other hand, the reason why the average aspect ratio of the porous body is set to be 50 or less is that a porous body composed of plate-shaped crystals with an average aspect ratio larger than 50 has few joints between the crystals, so the porous electric body itself This is because the strength is low. Among these, it is more preferable that the average aspect ratio of the plate crystals is 5 to aO, and the porous body of the present invention can be selected within this range depending on various uses.

By the way, conventionally, a sintered body having a structure in which plate crystals are relatively developed is, for example, US? , ? ! 1L4004984
and Journal Am@rican Ceram
ic 5ociety volume 59 pl), sss -48 (
1976).

However, the sintered body is a relatively densified silicon carbide sintered body, and the plate-like crystals are generated as the sintered body becomes densified. Therefore, the structure is completely different from a sintered body in which only plate crystals are developed as in the present invention.

Further, the average length of the plate crystals in the long sleeve direction is 0.5 to 1
It is necessary to belong to the genus 000μ. The reason for this is that when the average length in the long sleeve direction is smaller than 0.5 μm, the pores formed by the plate-like crystals are small, and in some cases, some of the pores may become independent pores, allowing fluid to pass through. This is because the resistance is large.

On the other hand, if the length is longer than 1000 μm, the strength of the joint between the plate crystals is low, and the strength of the porous electric body itself is low. Among them, the average length of the plate crystals in the long sleeve direction is 1 to
It is more preferable to have an island of 800 μm, and the porous body of the present invention can be selected within this range according to various uses. Note that the length of the plate-like crystals referred to here is the maximum length of each plate-like crystal observed in an arbitrary cross section of the sintered body.

The porous body of the present invention is characterized in that it has a transition layer in which the average cross-sectional area of pores in a three-dimensional network structure mainly composed of plate crystals changes continuously. The reason is that the porous body of the present invention can be used in applications such as filters to remove sludge mixed in plating solutions or foreign substances mixed in corrosive liquids such as sulfuric acid and hydrochloric acid. This is because foreign matter seeds contained in the fluid can be separated with high efficiency and quickly by passing the C fluid from the end surface side where the average cross-sectional area of the pores is large to the end surface side where the average cross-sectional area is small. . In addition, since the average cross-sectional area of the pores changes continuously, the particles collected inside the porous tube can be backwashed and removed, making it extremely easy to restore the function as a quill letter. be able to.

The transition layer defined in the present invention is a portion where the depletion rate of the flat cross-sectional area of the pores, that is, the value (V) expressed by the following equation (1), is at least 1.5.

v=vIT/L・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・(1) However, X: Ratio of the average cross-sectional area of pores existing on each of two arbitrary parallel planes.

(However, use the value of X-1.) L: Shortest distance #1 between any two parallel surfaces! (α) Also, the average cross-sectional area of the pores in the network structure is 0, O1-2
It is preferably within the range of 50,000 μR. The reason is that the average cross-sectional area of pores is 0. This is because when it is O1 μd or more, the passage resistance of the fluid is small.

On the other hand, if the average cross-sectional area of the pores is larger than 250,000μ, the strength of the porous electric body itself is low, and it is more advantageous that the average cross-sectional area of the pores in the network structure is between 0.25 and 90,000μ. It can be selected within this range depending on the use of the porous material tm of the present invention.

and 3 to 50 parts by weight of 100 parts by weight of crystals in the porous body.
The plate-like crystals having an aspect ratio of at least 20][preferably occupy the lid portion. Incidentally, the content of the plate crystals can be determined by analyzing a structural photograph of the crystals. Here, the porous body contains 20 parts or more of a to 50 parts by weight.
The reason why it is preferable that the plate crystals be occupied by plate crystals having an aspect ratio of This is because it is large. In particular, it is advantageous for the plate crystals to account for at least 40 parts by weight of 100 parts by weight of the crystals in the porous body.

The porosity of the three-dimensional network structure of the porous body is preferably 20 to 96% by volume based on the total g area of the sintered body. The reason for this is that when the porosity is less than 20% by volume, some of the pores tend to become independent pores, and the resistance when fluid passes through the porous body is large.On the other hand, when the porosity is more than 95% by volume, This is because although the resistance when a fluid passes through a porous body is small, the strength of the porous body is low, making it difficult to use. Advantageously, the amount is between 30 and 90% by volume.

The porous body of the present invention can be advantageously applied to applications such as oil-impregnated bearings and composite aggregates in addition to applications such as the filter mentioned above. It is advantageous to have a porous material that has a smaller average cross-sectional area and higher density of the pores in the outer wall to improve wear resistance, and a larger average cross-sectional area of the internal pores and higher porosity to improve oil receptivity. On the other hand, when applied as a composite aggregate, the average cross-sectional area of the pores in the center is made smaller and the density is increased to improve strength, while the average cross-sectional area of the outer pores is increased and the porosity is increased. A porous body with improved bonding properties with a mating material is advantageous. Also,
The porous body of the present invention may have a structure in which transition layers having a rate of change in the average cross-sectional area of the pores are alternately varied in different directions, if necessary.

Next, a method for producing a porous body having a three-dimensional network structure and a transition layer (hereinafter simply referred to as a pore transition layer) in which the average cross-sectional area of pores of the present invention changes continuously will be described.

According to the present invention, after a starting material consisting of silicon carbide powder with an average particle size of 10 μm or less is molded into a green body of a desired shape, the green body is charged into a heat-resistant container and exposed to outside air. When producing a porous body having pores with a three-dimensional network structure by firing within a range of 1700 to 2300°C while blocking penetration, one of the elements shown in the following group (1) or their compounds is used. A porous silicon carbide in which a transition layer in which the average cross-sectional area of the pores of the network structure continuously changes is formed by allowing at least one selected from the following to exist in the formed body so as to create a concentration gradient. A sintered body can be produced.

(1) Aluminum, boron, calcium, chromium, iron, lanthanum, lithium, titanium, yttrium, silicon, nitrogen, oxygen, back deposits.

According to the present invention, a 9M gradient is generated in the formed body by at least one selected from the elements shown in the above group (1) or their compounds (hereinafter simply referred to as transition layer forming aids). It is necessary to make it exist like this. The reason is that among the above substances, aluminum, boron,
Calcium, chromium, iron, lanthanum, lithium, titanium, and yttrium have the function of accelerating the growth rate of silicon carbide crystal grains, and where these substances exist, extremely large numbers of plate-like crystal nuclei are generated. As a result of the development of plate-like crystals in each part, the size of the plate-like crystals formed is limited, so areas where many of these substances exist should form a three-dimensional network structure with a very fine structure. On the other hand, among the above substances, silicon, nitrogen, oxygen, and carbon have the function of slowing down the crystal grain growth rate of silicon carbide, contrary to the above substances. Nucleation of plate crystals is suppressed where they exist, and the number of plate crystals formed is relatively small.As a result, each plate crystal grows relatively large, so many of these substances exist. This is thought to be because the locations can be formed into a three-dimensional network structure of a large tissue.

If the transition layer forming aid remains in a large amount in the sintered body, the original properties of silicon carbide will be lost, so it is best to minimize the amount of the transition layer forming aid remaining in the sintered body.
It is advantageous that the amount is 10 parts by weight or less per 00 parts by weight, and particularly preferably 5 parts by weight or less.

By the way, various methods can be applied to make the transition layer forming aid exist so as to create a concentration gradient within the formed body, but when forming a pore transition layer along the outer wall, for example, A method in which molded bodies having different contents of the transition layer forming aid are placed adjacent to each other on the outer wall of a portion of the formed body where the pore transition layer is intended to be formed, or a method of forming a pore transition layer of the formed body. It is advantageous to apply the transition layer forming aid to the outer wall of the desired location.On the other hand, when forming the pore transition layer inside, for example, when molding the formed body, apply the transition layer forming aid in advance. It is possible to apply a method of filling the transition layer forming aid 41 into a portion of the formed body where the purpose is to form a pore transition layer, or filling a silicon carbide powder with a different content of the transition layer forming aid 41. It's advantageous.

Various types of crystalline silicon carbide powders have been known in the past, but any of α-type crystals, β-type crystals, and amorphous silicon carbide powders can be used as a starting material for producing the porous body of the present invention. can be used.

However, particularly in porous materials having a large average cross-sectional area of pores, for example, the average cross-sectional area is 400 to 250,000 μm2.
When producing a porous body within the range of , silicon carbide powder with a total content of low temperature stable β type crystals, 2H type crystals and amorphous silicon carbide of at least 60% by weight is used as a starting material. It is advantageous to use

According to the present invention, the starting material needs to be a fine powder with an average particle size of 10 μm or less. Average particle size is 10μ
Powder smaller than m has a relatively large number of contact points between the particles, and at the firing temperature of silicon carbide, the thermal activity is large and the movement of atoms between silicon carbide particles is extremely large, so the silicon carbide particles Mutual bonding is extremely likely to occur, and the growth rate of plate crystals is extremely high. In particular, it is preferable that the average particle size of the starting material is 5 μIn or less, which gives more favorable results for the growth of plate-like crystals.

According to the present invention, after a starting material mainly composed of silicon carbide powder is molded into a formed body of a desired shape, the formed body is charged into a heat-resistant container and kept for 170 minutes while blocking the intrusion of outside air.
It is necessary to fire within the temperature range of 0 to 2800°C. The reason why the material is charged into a heat-resistant container and fired while cutting off the intrusion of outside air is that it is possible to fuse adjacent silicon carbide crystals and promote the growth of plate-shaped crystals. . The reason why it is possible to fuse adjacent silicon carbide crystals and promote the growth of plate-shaped crystals by charging them in a heat-resistant container and firing them while blocking the intrusion of outside air as described above is because the silicon carbide particles This is thought to be because the movement of silicon carbide between evaporation and recondensation and/or surface diffusion can be fully promoted. In contrast, when conventional pressureless sintering, atmospheric pressure sintering, or sintering under reduced pressure was tried, not only was it difficult to grow plate-shaped crystals, but the joints of silicon carbide particles were It has a constricted neck shape, which reduces the strength of the sintered body. As the heat-resistant container, it is more preferable to use a heat-resistant container made of at least one material selected from graphite, silicon carbide, tungsten carbide, molybdenum, and molybdenum carbide.

According to the invention, it is advantageous to charge the formed body into a heat-resistant container that can shut off outside air and fire it, so that the volatilization rate of silicon carbide during firing is 5 M% or less. be.

According to the invention, stomatal transitions with a relatively large rate of change! In order to obtain a porous body having II, it is advantageous to increase the concentration gradient of the transition layer forming auxiliary agent or to relatively increase the temperature increase rate during firing, while having a relatively small rate of change. In order to obtain a porous body having a pore transition layer, it is advantageous to reduce the concentration gradient of the transition layer forming aid and to increase the temperature during firing at a relatively slow rate. It is.

Further, according to the present invention, it is necessary to perform firing at a temperature range of 1700 to 2800°C. The reason for this is that the firing temperature is 1
If it is lower than 700'C, the growth of particles is insufficient and it is difficult to have a porous body with high strength.
This is because when the temperature is higher than 800"C, the sublimation of silicon carbide increases, and the developed plate-like crystals become thinner, making it difficult to obtain a porous body with high strength. Among these, firing at a temperature of 1800 to 2250°C is more preferable.

Next, the invention! lIi! This will be explained by examples and comparative examples.

Example 1 The silicon carbide fine powder used as the starting material was 94.6 fi
% consists of β-type crystals and the remainder consists essentially of 2H-type crystals,
0.89 wt% free carbon, 0.17 heavy metal oxygen, 0
．． It mainly contained 0.03% by weight of iron, 0.08% by weight of aluminum, and had an average grain size of 0.28μ.

To 100 M parts of the silicon carbide fine powder, 800 parts by weight of polyvinyl alcohol/v5 parts by weight were blended, and a bowl was prepared.
After mixing in Remi P for 5 hours, it was dried.

An appropriate amount of this dry mixture was taken, granulated, and then molded using a metal mold at a pressure of 50 kfl/eA.

The density of this product is 1.2 Vc4, and the dry weight is 21
It was no.

Next, the resulting formed body has a density of 98.6% and 0 boron.
．． The graphite crucible was placed on a plate-shaped dense silicon carbide containing 7% by weight and 0.05% by weight of aluminum, and placed in a graphite crucible that can be shut off from the outside air. Firing was performed in an argon gas atmosphere of 1 atm. The graphite crucible used had an internal volume of 5 (1+t).

For firing, the temperature was raised to 2200°C at a rate of 2.5°C/min and maintained at the maximum temperature of 2200°C for 6 hours.

The weight of the obtained sintered body was 19.6F, and its crystal structure was determined by the average cross section of the pores on the side in contact with dense silicon carbide, as shown in the scanning electron micrograph (75x magnification) in Figure 1. From the layer with a small area (layer A) to the layer with a large cross-sectional area of pores on the side opposite to the side in contact with dense silicon carbide (layer B), it increases by about 0.
It was found that there was a pore transition layer in which the average cross-sectional area of the pores continuously increased with the thickness of 4 silks, and the rate of change in the average cross-sectional area in the pore transition layer was about 200.

The characteristics of layer A and layer B are shown in Table 1.

Table 1 Using this porous material as a filter, from the B layer side to the A
Silicon carbide particles f with a particle size distribution of 0.4 to 100 μm toward the layer side
0.14kvf,/l of a suspension containing 5% by weight
When water was passed at a filtration pressure of -01, the initial water flow rate was 1O
09 Go'/Hr-Go, and 100% of this filter
Collection diameter is 0.8 tlrrL, 95% collection diameter is 0.5
μm:FM had excellent fitter characteristics.

Further, when this filter was used for 80 hours under the above conditions, the filtration pressure increased to 1.1 kyf/eA, but was able to almost recover.

Comparative Example 1 A porous body was obtained by sintering in the same manner as in Example 1, but without using dense silicon carbide.

The weight of the obtained sintered body was 19.1', and it had a three-dimensional network structure in which plate-shaped crystals with an average aspect ratio of 12 and an average length in the major axis direction of 880 μm were intricately intertwined in multiple directions. The content of plate crystals having an aspect ratio of 3 to 5G was 98% of the total weight of the porous tube. Further, the open porosity of this porous body was 64% of the total volume, and the average cross-sectional area of the open pores was 72,500 μm.

Next, 5J! When a filtration test was conducted in the same manner as in Example 1, the 100% collection diameter was 15 μm and the 195% collection diameter was 8
μm+1, and when water was passed at a transient pressure of 0.14 kgfM, the initial water flow rate was 14.1 td/Hr-m.
'Met.

Comparative Example 2 A method similar to Example 1, but using 95% as the starting material.
8% by weight consists of β-type crystals and the rest consists of 2H-type crystals, 0.32fl amount% free allj2 element, 0.15% blood amount oxygen, 0.03% iron, O, Oa weight aluminum in the form, mainly containing 0.5% by weight of boron,
Using silicon carbide fine powder with an average particle size of 0.0027 μm, the temperature was raised to 2200"C at a heating rate of 7.5°C/i and held at the maximum temperature of 2200"C for 3 hours to form a sintered body. Obtained.

The weight of the obtained sintered body was 19. It has a three-dimensional network structure in which plate-like crystals with an average aspect ratio of 7 and an average length in the major axis direction of 25μ are intricately intertwined in multiple directions, and have an aspect ratio of 3 to 50. The content of plate crystals was 95% of the total weight of the porous tube. Further, the open porosity of this porous body was 57% of the total volume, and the average cross-sectional area of open pores was 760 μm.

Next, a filtration test was conducted in the same manner as in Example 1, and the 100% collection diameter was O.a.mu.m, and the 95% collection diameter was 0.a.mu.m.
When the filter was filtered with oil and water at a filtration pressure of 0.14 #μd, the initial water flow rate was 8.4 Ml/Hr-n/.

Also, according to this filtration test, the filtration pressure increased to 1 in about 4 hours.
．． It has increased to 1#μ-.

Example 2 The surface of a green body molded in the same manner as in Example 1 was sprinkled with boron nitride powder, placed in a graphite crucible, and heated at 5°C/i.
The temperature was raised to 2150℃ at a heating rate of
A sintered body was obtained by holding at C for 4 hours.

The weight of the obtained sintered body was 19.61, and it was released.

The porosity was 58% of the total volume. Its crystal structure is such that a layer with a thickness of about 0.5H and a small average cross-sectional area of pores is formed from the surface to the inside, and then about 0.5H thick toward the inside.
It was found that there was a pore transition layer with a thickness of 411j in which the average cross-sectional area of the pores was continuously increasing, and the rate of change in the average cross-sectional area in the pore transition layer was about 180. The characteristics of each part are shown in Table 2.

Table 2 This sintered body was processed into a ring shape with an outer diameter of 8011 IJ+1 and an inner diameter of 15 mm, and then impregnated with spindle oil.

Next, this porous body stainless steel w4 (SUS804
) was carried out using the ring-on-ring method at a sliding speed of 15 i/see with an end face load of 10 &fμ-, and the friction coefficient was 0, 1 to 0.12.
It was found that the material had extremely good sliding properties. The amount of wear after approximately 1000 hours of sliding test was 0.4 for both partners.
It was extremely small, µm.

Example 3 Same as Example 1, but when molding the formed body,
2.5% of the dry mixture used in Example 1 was applied to a metal mold.
1. Subsequently, 5f of the dry mixture used in Comparative Example 2 and finally 2.5f of the dry mixture used in Example 1 were charged, and after preforming at a pressure of 50 kg/ed, 1800
Hydrostatic pressing was performed at a pressure of #/d. The resulting green body had a diameter of 40 fl and a thickness of 30,111 mm.

Next, the resulting green body was placed in a graphite crucible that can block the intrusion of outside air, and fired in an argon gas atmosphere at 1 atm using a Tammann type firing furnace. The graphite crucible used had an internal volume of 50 m.

For firing, the temperature was raised to 2100°C at 5°C/m, and the temperature was increased to 2100°C.
It was held at C for 4 hours. Then another 2.5°C/xi
The temperature was raised to 2200° C. at 2200° C. and held at 2200” C for 2 hours.

The obtained sintered body has a diameter of about 0.601 from the surface to the inside.
11, a layer with a large average cross-sectional area of pores is formed,
Furthermore, there is a pore transition layer in which the average cross-sectional area of the pores decreases continuously with a thickness of about 0.7 gml toward the inside, and the rate of change in the average cross-sectional area in the pore transition layer is about 197 gml. It was recognized that Note that the characteristics of the surface layer portion and the center portion are shown in Table 8.

Table 3 [Effects of the Invention] As described above, the porous body of the present invention in which the size of the complete pore diameter is continuously changed can be used in a high temperature atmosphere, an oxidizing atmosphere, and/or an oxidizing atmosphere.
It is also an excellent material for industrial applications such as filtration filters used in corrosive atmospheres, catalysts or catalyst supports for oxidative dusting reactions or chemical reactions at high temperatures, sliding materials, and aggregates for composites. Extremely useful.

[Brief explanation of drawings]

Figure 1 is a scanning electron micrograph (75x magnification) showing the crystal structure of the sintered body described in Example 1, and Figure 2 is a schematic diagram showing the structure of the porous silicon carbide sintered body obtained by the conventional method. be. A...Silicon carbide aggregate, B...Binder,
C: Gaps in the porous body.

Claims (1)

[Scope of Claims] 1. A sintered body mainly made of silicon carbide, having an average aspect ratio within the range of 3 to 50 and an average length in the major axis direction within the range of 0.5 to 1000 μm. A porous material having a three-dimensional network structure mainly composed of silicon carbide plate-like crystals, and having a transition layer in which the average cross-sectional area of open pores of the network structure changes continuously. High quality silicon carbide sintered body. 2. The porous silicon carbide sintered body according to claim 1, wherein the average cross-sectional area of the open pores of the network structure of the porous silicon carbide sintered body is within the range of 0.01 to 250000 μm^2. 3. 3 to 100 parts by weight of the porous silicon carbide sintered body
Plate crystals with an aspect ratio of 50 are at least 20
The porous silicon carbide sintered body according to claim 1 or 2, which is in parts by weight. 4. The porous silicon carbide sintered body according to any one of claims 1 to 3, wherein the open porosity of the network structure is 20 to 95% by volume based on the total volume of the sintered body. 5. After molding the starting material mainly consisting of silicon carbide powder with an average particle size of 10 μm or less into a green body of a desired shape, the green body is placed in a heat-resistant container to block the intrusion of outside air. When producing a porous silicon carbide sintered body having open pores with a three-dimensional network structure by firing within a temperature range of 1,700 to 2,300°C, one of the elements shown in the following group (1) or their compounds may be used. A porous material characterized in that at least one selected from the following is present so as to create a concentration gradient within the formed body, forming a transition layer in which the average cross-sectional area of the open pores of the network structure changes continuously. A method for producing a silicon carbide sintered body. (1) Aluminum, boron, calcium, chromium, iron, lanthanum, lithium, titanium, yttrium, silicon, nitrogen, oxygen, carbon. 6. The porous silicon carbide sintered body has an average aspect ratio in the range of 3 to 50 and an average length in the major axis direction of 0.5 to 10.
It has a three-dimensional network structure mainly composed of silicon carbide plate crystals with a diameter of 0.00 μm, and the average cross-sectional area of open pores in the network structure is 0.01 to 250000 μm^2.
The manufacturing method according to claim 5, which is within the scope of.